precipitation · South Africa
Cape Town, Western Cape
May–August winter rainfall total
Modelled demonstration series · not observed data
A city with one rainy season has one opportunity to refill, and this chart is that opportunity missed. Three consecutive years like this is what produced Day Zero planning here — the point at which municipal taps would have been shut off and water rationed from collection points. The failure mode is not drought, it is consecutive drought.
75 years, modelled
Same reading, two normals
| Normal | Mean | σ | Pct | Return |
|---|---|---|---|---|
| 1951–1980 | 420 mm | −2.90σ | 0.19th | 1 in 540 years |
| 1991–2020 | 353 mm | −2.38σ | 0.87th | 1 in 120 years |
Today would be the lowest value in the entire 75-year modelled series. Past the series' standing low of 239 mm (2001). Nothing about the reading changes between rows — only the yardstick.
The season here
Cape Town is a winter-rainfall city. Everything the reservoirs get, they get between May and August — there is no second chance in summer.
Where this series comes from
MODELLED SERIES — not observed. Parameters set from published Cape Town winter-rainfall climatology and the documented drying trend in the south-western Cape; lognormal transform applied. The 75 annual values are synthesised by the seeded generator.
Every number on this page comes from a modelled series: 75 annual values synthesised by a seeded generator from published climatological parameters for Cape Town, Western Cape. It shows how anomaly reasoning works. It is not a measurement and must not be cited as one.
How to read σ
σ counts standard deviations from this place's own normal. The sigma guide · return periods.
More precipitation stations
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